The present invention relates to apparatus and methods for chemical mechanical polishing a substrate, and more particularly to such apparatus and methods using a moving polishing sheet.
An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a patterned stop layer, and planarizing the filler layer until the stop layer is exposed. For example, trenches or holes in an insulative layer may be filled with a conductive layer. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs and lines that provide conductive paths between thin film circuits on the substrate.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a xe2x80x9cstandardxe2x80x9d pad or a fixed-abrasive pad. A standard pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles if a standard pad is used, is supplied to the surface of the polishing pad.
An effective CMP process not only provides a high polishing rate, but also provides a substrate surface which is finished (lacks small-scale roughness) and flat (lacks large-scale topography). The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad. The polishing rate sets the time needed to polish a layer, which in turn sets the maximum throughput of the CMP apparatus.
During CMP operations, the polishing pad needs to be replaced periodically. For a fixed-abrasive pad, the substrate wears away the containment media to expose the embedded abrasive particles. Thus, the fixed-abrasive pad is gradually consumed by the polishing process. After a sufficient number of polishing runs the fixed-abrasive pad needs to be replaced. For a standard pad, the substrate thermally and mechanically damages the polishing pad and causes the pad""s surface to become smoother and less abrasive. Therefore, standard pads must be periodically xe2x80x9cconditionedxe2x80x9d to restore a roughened texture to their surface. After a sufficient number of conditioning operations (e.g., three hundred to four hundred), the conditioning process consumes the pad or the pad is unable to be properly conditioned. The pad must then be replaced.
One problem encountered in the CMP process is difficulty in replacing the polishing pad. The polishing pad may be attached to the platen surface with an adhesive. Significant physical effort is often required to peel the polishing pad away from the platen surface. The adhesive then must be removed from the platen surface by scraping and washing with a solvent. A new polishing pad can then be adhesively attached to the clean surface of the platen. While this is happening, the platen is not available for the polishing of substrates, resulting in a decrease in polishing throughput.
In one aspect, the invention is directed to a chemical mechanical polishing apparatus that has a platen, a polishing sheet extending between the a first reel and a second reel, and a motor to drive at least one of the first and second reels to move the polishing sheet in a linear direction across the top surface of the platen during polishing. The polishing sheet has a width greater than a diameter of a substrate to be polished and has a portion extending over a top surface of the platen for polishing the substrate.
Implementations of the invention may include the following. The motor may drive the first and second reels in a first direction to transfer the polishing sheet from the first reel to the second reel, and in a second direction to transfer the polishing sheet from the second reel to the first reel. A controller may cause the motor to alternate between driving the first and second reels in the first and second directions. The controller may be configured to cause the motor to decelerate when one of the first and second reels is nearly empty. Also, the controller may be configured to cause the motor to accelerate until the polishing sheet is moving at a desired speed, e.g., about one meter per second. The platen may include a plurality of passages to provide fluid to a top surface of the platen and create a fluid bearing between the polishing sheet and the platen. A fluid source may be fluidly coupled to the plurality of passages. An actuator may move the platen, which may be generally rectangular in shape, toward and away from the polishing sheet. A rotatable carrier head may hold the substrate. A frame and a plurality of retainers may secure the first and second reels to the frame. The polishing sheet may be a generally linear strip of a fixed abrasive polishing material.
In another aspect, the invention is directed to a chemical mechanical polishing apparatus that has a platen, a first roller, a second roller, a generally linear polishing sheet extending between the first and second rollers, and a motor to drive at least one of the first and second rollers to transfer the polishing sheet between the first and second rollers and move the polishing sheet in a linear direction across the top surface of the platen. The polishing sheet has a width greater than a diameter of a substrate to be polished. The polishing sheet has a first portion wound around the first roller, a second portion wound around the second roller, and a third portion extending over a top surface of the platen to polish the substrate.
In another aspect, the invention is directed to a chemical mechanical polishing apparatus that has a platen, a first roller, a second roller, a polishing sheet extending between the first and second rollers, a motor to drive the first and second rollers to move the polishing sheet across the top surface of the platen, and a controller to cause the motor to alternately drive the polishing sheet in a first direction and a second, opposing direction during polishing of the substrate. The polishing sheet has a width greater than a diameter of a substrate to be polished and has a portion extending over a top surface of the platen for polishing the substrate.
In another aspect, the invention is directed to a method of chemical mechanical polishing in which a substrate is brought into contact with a polishing sheet that extends between a first reel and a second reel, and the first and second reels are driven to move the polishing sheet in a linear direction across a top surface of a platen during polishing. The polishing sheet has a width greater than a diameter of a substrate to be polished.
Implementations of the invention may include the following. The first and second reels may alternate between being driven in a first direction to transfer the polishing sheet from the first reel to the second reel, and in a second direction to transfer the polishing sheet from the second reel to the first reel. The first and second reels may decelerate when one of the first and second reels is nearly empty. The first and second reels may accelerate until the polishing sheet is moving at a desired speed, e.g., about one meter per second. A fluid may be injected between a top surface of the platen and the polishing sheet to create a fluid bearing therebetween. The platen may be moved vertically to adjust a pressure of the polishing sheet on the substrate. The substrate may be rotated. The polishing sheet may be a fixed abrasive polishing material. A fluid may be injected between a surface of the substrate and the polishing sheet through holes in the polishing sheet.
Advantages of the invention may include the following. More substrates can be polished without replacing the polishing pad, thereby reducing downtime of the CMP apparatus and increasing throughput. A sheet of fixed-abrasive polishing material can be provided in a polishing cartridge. It is easy to remove and replace the polishing cartridge from a platen. The polishing apparatus gains the advantages associated with fixed-abrasive polishing materials. A rotating carrier head can be used to press the substrate against the polishing sheet. Lateral frictional forces on the substrate can be reduced, thereby decreasing the load of the substrate against the retaining ring and improving polishing uniformity. The rigidity of the polishing sheet against the substrate can be adjusted independent of the polishing sheet material.
Other features and advantages will be apparent from the following description, including the drawings and claims.